The proposed research is designed to determine the physiological and pathophysiological factors involved in the interaction between dietary sodium intake and environmental stress in relation to the pathogenesis of hypertension. A major focus is that dietary sodium intake modulates the efferent renal sympathetic nerve activity (ERSNA) response to environmental stress and that the resultant changes in renal hemodynamic and excretory function contribute importantly to the development, maintenance and exacerbation of hypertension. Using techniques for measurements of ERSNA and renal function in conscious hypertensive rate models, the interaction between genetic and environmental (dietary sodium/potassium intake, environmental stress) factors will be examined. Specific Aim 1 will determine if the sensitivity of central nervous system alpha-2 adrenoceptors involved in the regulation of the ERSNA response to environmental stress is affected by changes in dietary sodium intake. Specific Aims 2 and 3 will determine if acute exposure to environmental stress increases ERSNA and decreases urinary sodium excretion in Dahl R/S and Borderline Hypertensive Rats (BHR). Specific Aim 4 will determine if high dietary sodium intake modulates the ERSNA and renal hemodynamic/excretory response to environmetal stress in BHR. Specific Aim 5 will determine if the enhanced ERSNA and renal hemodynamic/excretory responses to environmental stress in SHR on a high dietary sodium intake are dependent on increases in total body sodium and fluid volumes. Specific Aim 6 will determine if dietary potassium supplementation modulates the ERSNA and renal hemodynamic/excretory responses to environmental stress in experimental forms of hypertension.